balaclava vs head covering

balaclava

noun
  • A type of warm headgear covering the neck, head, and often part of the face, with apertures left as necessary, often made out of wool. 

  • A ski mask with holes for the eyes and, sometimes, the nose and mouth, which may be rolled up and worn like a toque or pulled over the face for greater protection. 

head covering

noun
  • A covering for the head. 

How often have the words balaclava and head covering occurred in a corpus of books? (source: Google Ngram Viewer )